amcheck: Add a test with GIN index on JSONB data

amcheck: Add a test with GIN index on JSONB data

Extend the existing test of GIN checks to also include an index on JSONB
data, using the jsonb_path_ops opclass. This is a common enough usage of
GIN that it makes sense to have better test coverage for it.

Author: Mark Dilger <mark.dilger@enterprisedb.com>
Reviewed-By: Tomas Vondra <tomas.vondra@enterprisedb.com>
Reviewed-By: Kirill Reshke <reshkekirill@gmail.com>
Discussion: https://postgr.es/m/BC221A56-977C-418E-A1B8-9EFC881D80C5%40enterprisedb.com